A fluid resistance device implies a device having a flow passage (also referred to as “resistance flow passage” hereinafter) acting as a resistance when fluid flows therein and a flow rate of the fluid can be measured based on pressures in an upstream side and a downstream side thereof when the fluid is directed to flow through this fluid resistance device.
For example, in the case of a flow control device for controlling a flow rate of material gas used for manufacturing a semiconductor, the fluid resistance device for use therein is required to have a very fine accuracy in controlling the flow rate, and a resistance flow passage is required to have a thickness of several tens of microns in some cases.
Therefore, for example, in Patent Literature 1, there is disclosed a configuration such that upper and lower sides of an annular slit plate having a thickness of several tens of microns which is radially formed with a plurality of slits are covered with circular cover plates so that each of the slit portions serves as a resistance flow passage. In this configuration, the slit plate together with the cover plates is held and fixed between upper and lower fixing plates via seal members such as O-rings from further upper and lower sides of the cover plates.
However, when the fixing plates hold the cover plate therebetween, stresses are concentrated at a contact portion between the O-ring and the cover plate and there occurs a slight deflection in the cover plate having a thickness of several tens of microns. Thus, the resistance characteristics of the fluid resistance device are changed by a slight error of an applied power adjustment when holding the cover plate between the fixing plates. Therefore, it becomes difficult to stably manufacture the fluid resistance device having uniform resistance characteristics. In some cases, there may be also a problem that the cover plate is largely deflected and the resistance flow passage would be completely crushed and the fluid would not be able to flow in the resistance flow passage.